The present invention relates to an electronic device for controlling the air/fuel ratio of the mixture supplied to an internal-combustion engine.
Electronic devices for controlling the air/fuel ratio in a closed loop are known, in which an oxygen sensor of the ON/OFF type, advantageously consisting of a lambda probe and arranged in the exhaust manifold of an internal-combustion engine (in particular a petrol engine), generates a bistable feedback signal, the state of which depends on the relationship existing between the air/fuel ratio of the mixture supplied to the engine and the stoichiometric air/fuel ratio.
In particular, lambda probes of the known type are designed to generate a first output voltage, for example ranging between 450 and 900 mVolt, when the mixture supplied to the engine has more fuel than is required by the stoichiometric ratio (rich state) and a second output voltage, for example ranging between 100 and 450 mVolt, when the mixture supplied to the engine has less fuel than is required by the stoichiometric ratio (lean state). Control devices of known type are designed to supply the feedback signal to a processing circuit, in particular a proportional integral (P.I.) circuit which generates at its output a correction parameter KO2 which is used to modify, in a closed loop, the value of a parameter calculated in an open loop and representing a quantity of fuel to be injected. Known ratio control devices produce, by means of the feedback of the signal generated by the lambda probe, an oscillation of the air/fuel ratio actually supplied to the engine about the stoichiometric value; this oscillation takes place within a predetermined range defined by upper and lower limits and allows correct operation of the catalytic converter arranged along the exhaust pipe downstream of the lambda probe.
Linear oxygen sensors, for example so-called UEGOs (Universal Exhaust Gas Oxygen Sensors), designed to generate at their output a signal proportional to the concentration of oxygen present in the exhaust gases, are also known.